1. Field of the Invention
This invention relates to means for enhanced recovery of podophyllotoxin from biological sources for its pharmaceutical use or as an intermediate in the production of antineoplastic agents.
2. Description of the Prior Art
The aryltetralin lignan podophyllotoxin is used as the starting material for the semisynthesis of the antineoplastic agents etopside and teniposide. It has also been recognized as possessing antitumor and antimitotic activities of its own. Podophyllotoxin is a natural product found in Podophyllum spp. (Berberidaceae). The main commercial source of podophyllotoxin is P. emodii Wall. (syn. P. hexandrum Royale), found in alpine and sub-alpine areas of the Himalayas. P. emodii has been declared an endangered species as a result of overcollection of the native population. Given the increasing medicinal importance of podophyllotoxin-derived drugs, attempts have been made to develop alternative and renewable sources for this compound. This has included the domestication and in vitro culture of P. emodii, the evaluation of wild harvested, cultivated and in vitro propagated P. peltatum (a plant native to North America commonly known as mayapple), and the utilization of other aryltetralin lignan-producing species.
Commercial production of podophyllotoxin involves its purification from an ethanolic extract of the dried roots and rhizomes of P. emodii, which is commercially known as Podophyllum resin or podophyllin. This resin is obtained by percolation of warm ethanol through the dried plant material, followed by precipitation with a dilute acid. Known analytical methods similarly involve extraction of the dried plant material with ethanol. Through use of these methods, the podophyllotoxin content of rhizomes and roots of P. emodii has been measured at 4.3% of the dry weight (Jackson et al., 1984, Aryltetralin lignans from Podophyllum hexandrum and Podophyllum peltatum, Phytochemistry 23:1147-1152). Rhizomes and leaves of P. peltatum have been found to respectively contain up to 0.26% and 0.54% podophyllotoxin, along with varying amounts of other aryltetralin lignans and their glycosides (Bastos et al., 1996, Quantitation of aryltetralin lignans in plant parts and among different populations of Podophyllum peltatum by reverse phase high performance liquid chromatography, Journal of Natural Products 59:406-408). Alternate approaches to recovering podophyllotoxin have included purely synthetic approaches (Takeya et al., 1984, Biomimetic Synthesis of Podophyllum Lignans, Chem. Pharm. Bull., 32(1): 31-37) and extraction methods making use of supercritical carbon dioxide (Choi et al.,1998, Supercritical Carbon Dioxide Extraction of Podophyllotoxin from Dysosmia pleiantha Roots, Planta Medica 64:482-483).
While methodologies exist for synthesis or recovery of podophyllotoxin, there remains a need for the creation of new cost-effective and sustainable methods for providing a dependable long-term supply of this material.